188 CLASS CRUSTACEA. 



moreover, is much more considerable. The peduncle of the 

 lateral antenna is accompanied with a scale, or spines ; the 

 external leaf of the lateral fins of the end of the tail is, in all 

 the living species, as it were, divided into two by a transverse 

 suture. 



Eryon, Desm., 



Have all the leaflets of the caudal fin, narrowed at their ex- 

 tremity, and terminating in a point ; the exterior one presents 

 no transverse suture ; the two threads of the middle antennae 

 are very short, and scarcely longer than their peduncle ; the 

 sides of the testa have very deep notches ; the forceps of 

 the two anterior claws are narrow and elongated. [Eryon 

 Cuvierii, Desm., a fossil species.) 



AsTACUS, Gronov., Fab., 



Have the leaflets of the lateral fins of the end of the tail 

 widened and rounded at their extremity ; the external one is 

 divided transversely into two by a transverse suture, the pos- 

 terior extremity of that of the middle is obtuse or rounded ; 

 the two threads of the middle antennae are notably longer than 

 their peduncle ; the sides of the testa are not incised. 



In some, and all marine, the last segment of the tail, or that 

 which occupies the middle of the terminal fin, presents no 

 transverse suture. 



Those whose lateral antennae have a large scale on the 

 peduncle, whose eyes are very large, and kidney-formed, and 

 in which the pincers of the two anterior claws are narrow, 

 elongated, prismatic, and equal, foi-m the genus Nephrops 

 of Dr. Leach. [Cancer Norivegicus, Linn.) 



Those in which the peduncle of the lateral antennae presents 

 simply but tv\'o short projections, in the form of teeth or 

 spines, whose eyes are neither very large nor reuiform, and 

 w^hich have the pincers or forceps more or less oval, com- 



